Reciprocating pump with improved fluid cylinder cross-bore geometry

ABSTRACT

A reciprocating pump comprising a fluid end housing having a number of plunger sections, each of which includes a plunger bore within which a plunger is slidably received, a suction bore within which a suction valve is positioned, a discharge bore within which a discharge valve is positioned, and a cross bore chamber which is located between said bores and is configured as a surface of revolution. Each of the bores intersects the cross-bore chamber to thereby define a respective cross curve which is spatially separated from each adjacent cross curve. In this manner, the cross-bore chamber defines a single, contiguous surface which extends around and between all of said cross curves.

BACKGROUND OF THE INVENTION

The present invention is related to reciprocating plunger andpiston-type pumps which are used, for example, in oil well serviceoperations. In particular, the invention is related to an improvedcross-bore geometry for the fluid end of such pumps.

Plunger pumps for the oilfield industry typically include a power endand a fluid end. The fluid end generally includes a plunger which ispositioned in a plunger bore and is reciprocated by the power end, anaccess bore which is located opposite the plunger bore, a suction valvewhich is positioned in a suction bore and a discharge valve which ispositioned in a discharge bore. In operation, the plunger isreciprocated in the plunger bore to alternately draw fluid into the pumpthrough the suction valve and then force the fluid out of the pumpthrough the discharge valve.

During operation of the pump, the fluid end is subject to very highfrequency and large magnitude pressure pulsations. These pressurepulsations generate large stress concentrations at the intersections ofthe bores. In cross-bore geometries in which the bore intersections formrelatively sharp edges, these stress concentrations may cause fatiguecracks to form in the fluid end proximate the intersections. In someprior art pumps, the intersecting edges of the bores are machined tohave quasi radii and chamfered features in an attempt to smooth the boreintersections. Although smoothing the bore intersections in this mannermay reduce the stress concentrations to a certain extent, the cross-boregeometries of extreme service pumps remain susceptible to developingexcessive stress concentrations due to the limitations imposed by thecurrent configurations of the bore intersections.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other limitations inthe prior art are overcome by providing a reciprocating pump comprisinga fluid end housing having a number of plunger sections, each plungersection including a plunger bore within which a plunger is slidablyreceived, a suction bore within which a suction valve is positioned, adischarge bore within which a discharge valve is positioned, and a crossbore chamber which is located between said bores and is configured as asurface of revolution. Each of said bores intersects the cross-borechamber to thereby define a respective cross curve which is spatiallyseparated from each adjacent cross curve. In this manner, the cross-borechamber defines a single, contiguous surface which extends around andbetween all of said cross curves.

In accordance with one embodiment of the invention, the cross-borechamber is configured as an ellipsoid. In this embodiment, the ellipsoidmay comprise a first axis which is coaxial with a centerline of theplunger bore and a second axis which is coaxial with at least one of acenterline of the suction bore and a centerline of the discharge bore.Alternatively, the ellipsoid may comprise a first axis which is coaxialwith a centerline of the plunger bore and a second axis which isparallel to but offset from at least one of a centerline of the suctionbore and a centerline of the discharge bore. Alternatively, theellipsoid may comprise a first axis which is parallel to but offset froma centerline of the plunger bore and a second axis which is coaxial withat least one of a centerline of the suction bore and a centerline of thedischarge bore. Alternatively, the ellipsoid may comprise a first axiswhich is parallel to but offset from a centerline of the plunger boreand a second axis which is parallel to but offset from at least one of acenterline of the suction bore and a centerline of the discharge bore.

In accordance with another embodiment of the invention, each plungersection further comprises an access bore which intersects the cross-borechamber to thereby define a corresponding cross curve that is spatiallyseparated from each adjacent cross curve. In this manner, the cross-borechamber defines a single, contiguous surface which extends around andbetween all of said cross curves. In this embodiment, the cross-borechamber may be configured as an ellipsoid. In addition, the access boremay be generally aligned with the plunger bore and the suction bore maybe generally aligned with the discharge bore, and the access and plungerbores may be oriented at an angle of generally ninety degrees relativeto the suction and discharge bores. Also, the ellipsoid may comprise afirst axis which is coaxial with a centerline of the plunger bore and asecond axis which is coaxial with at least one of a centerline of thesuction bore and a centerline of the discharge bore. Alternatively, theellipsoid may comprise a first axis which is coaxial with a centerlineof the plunger bore and a second axis which is parallel to but offsetfrom at least one of a centerline of the suction bore and a centerlineof the discharge bore. Alternatively, the ellipsoid may comprise a firstaxis which is parallel to but offset from a centerline of the plungerbore and a second axis which is coaxial with at least one of acenterline of the suction bore and a centerline of the discharge bore.Alternatively, the ellipsoid may comprise a first axis which is parallelto but offset from a centerline of the plunger bore and a second axiswhich is parallel to but offset from at least one of a centerline of thesuction bore and a centerline of the discharge bore.

In accordance with a further embodiment of the invention, the plungerbore, the suction bore and the discharge bore are oriented at an angleof approximately 120 degrees relative to each other. In this embodiment,the ellipsoid may comprise a first axis which is coaxial with acenterline of the plunger bore and a center point which is located at anintersection of the plunger bore, the suction bore and the dischargebore. Alternatively, the ellipsoid may comprise a first axis which iscoaxial with a centerline of the plunger bore and a center point whichis offset from an intersection of the plunger bore, the suction bore andthe discharge bore. Alternatively, the ellipsoid may comprise a firstaxis which is parallel to but offset from a centerline of the plungerbore and a center which is located at an intersection of the plungerbore, the suction bore and the discharge bore. Alternatively, theellipsoid may comprise a first axis which is parallel to but offset froma centerline of the plunger bore and a center which is offset from anintersection of the plunger bore, the suction bore and the dischargebore.

The present invention is also directed to a method of reducing stressconcentrations in a fluid end housing of a reciprocating pump, the fluidend housing having a number of plunger sections, each plunger sectionincluding a plunger bore within which a plunger is slidably received, asuction bore within which a suction valve is positioned and a dischargebore within which a discharge valve is positioned. The method comprisesforming a cross-bore chamber between said bores, said cross-bore chamberbeing configured as a surface of revolution, wherein each of said boresintersects the cross-bore chamber to thereby define a respective crosscurve which is spatially separated from each adjacent cross curve. Inthis manner, the cross-bore chamber defines a single, contiguous surfacewhich extends around and between all of said cross curves. In accordancewith one aspect of this embodiment, the cross-bore chamber may beconfigured as a spheroid.

Thus, in accordance with the present invention an improved cross-boregeometry is obtained by creating a cross-bore chamber at theintersection of the plunger bore, the suction bore, the discharge boreand, if present, the access bore. The cross-bore chamber is configuredas a surface of revolution which is created by rotating atwo-dimensional curve around a reference axis. For example, thecross-bore chamber may be configured as an ellipsoid, a particular caseof which is a sphere. By configuring the cross-bore chamber as a surfaceof revolution such as an ellipsoid, the cross-bore chamber provides asingle, smooth contiguous connecting surface between the bores. As aresult, the stress concentrations in the cross-bore geometry aresignificantly reduced, and the fluid end is therefore less susceptibleto failure.

These and other objects and advantages of the present invention will bemade apparent from the following detailed description, with reference tothe accompanying drawings. In the drawings, the same reference numbersare used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partial cut-away view of a prior art plungerpump in which the cross-bore geometry of the present invention may beincorporated;

FIG. 2 is a cross sectional view of the fluid end of the plunger pumpshown in FIG. 1;

FIG. 3 is a cross sectional view similar to FIG. 2 but with the internalcomponents of the fluid end removed for clarity;

FIG. 4 is a schematic representation of the cross bore geometry inaccordance with one embodiment of the present invention;

FIG. 5 is a perspective, cut-away view of an embodiment of a fluid endof the present invention having an illustrative cross bore geometry;

FIG. 6 is a cross sectional view of the fluid end shown in FIG. 5;

FIGS. 7-9 are cross sectional views of additional embodiments of fluidends having differing illustrative cross-bore geometries; and

FIG. 10 is a cross sectional view of another embodiment of a fluid endin which the cross-bore geometry of the present invention may beincorporated.

DETAILED DESCRIPTION OF THE INVENTION

An example of a prior art plunger pump in which the cross-bore geometryof the present invention may be incorporated is shown in FIG. 1. Asdescribed more fully in U.S. Pat. No. 7,610,847, which is herebyincorporated herein by reference, the plunger pump 10 comprises a powerend 12 and a fluid end 14. The power end 12 includes a gear reducerassembly 16 which is driven by a suitable motor (not shown). The gearreducer assembly 16 drives a crankshaft 18. The crankshaft 18 isrotatably connected to one end of a connecting rod 20, the opposite endof which is pivotally connected to a crosshead 22 that is supported forlinear movement in a corresponding guide bore 24. The fluid end 14includes a number of plungers 26 (only one of which is shown in FIG. 1),each of which is slidably mounted in a respective plunger bore 28 and isconnected to a respective crosshead 22 by a plunger rod 30. Inoperation, rotary motion of the crankshaft 18 is converted by theconnecting rod 20 into linear reciprocating motion of the crosshead 22,which in turn reciprocates the plunger 26 in the plunger bore 28.

The fluid end 14 comprises a laterally extending housing 32 having anumber of plunger sections (in this case five) which are each alignedwith a corresponding plunger 26. The middle plunger section is shown ingreater detail in FIGS. 2 and 3. With the exception noted below, themiddle plunger section is similar to the remaining plunger sections. Asdescribed more fully in U.S. Pat. No. 7,681,589, which is herebyincorporated herein by reference, the middle plunger section includes across bore arrangement comprising the plunger bore 28, an access bore 34which is generally aligned with the plunger bore, a suction bore 36which is generally perpendicular to the plunger bore, and a dischargebore 38 which is generally aligned with the suction bore.

The plunger 26 is positioned in the plunger bore 28 and is sealedthereto by, e.g., an annular packing 40, which in the embodiment shownin FIG. 2 is mounted in a stuffing box 42 that is secured to the housing32 by a number of cap screws 44. The access bore 34 is sealed by a plug46 which is secured to the housing 32 by a first retainer nut 48. Asuction valve 50 is positioned in the suction bore 36 between theplunger bore 28 and an inlet port 52. A discharge valve 54 is positionedin the discharge bore 38 between the plunger bore 28 and a pressure tapfitting 56 which is secured in the discharge bore by a second retainernut 58. The discharge bores 38 of the remaining bore sets are sealed byplugs 60 (FIG. 1) similar to the plug 48 (FIG. 2), and all of thedischarge bores are fluidly connected via a lateral bore 62 to an outletcoupling 63 (FIG. 1). In this manner, all the fluid pumped through theseveral plunger sections will be directed through the lateral bore 62and exit the pumping unit 10 through the outlet coupling 63.

As shown in FIG. 1, the inlet ports 52 of the several plunger sectionsare connected to an inlet manifold 64 having a pump inlet 66 which isconnectable to, e.g., a source of well service fluid (not shown). Inoperation of the plunger pump 10, the plungers 26 are reciprocated bythe power end 12 in the manner described above. During the suctionstroke of each plunger 26, the suction valve 50 is forced open and fluidis drawn through the suction bore 36 and into the plunger bore 28.During the discharge stroke of each plunger 26, the suction valve 50 isforced closed and the fluid in the plunger bore 28 is forced through thedischarge valve 54 and the outlet coupling 63. Further details of theoperation of the suction valve 50 and the discharge valve can be foundin the aforementioned U.S. Pat. No. 7,681,589.

The cross bore arrangement of each plunger section is shown more clearlyin FIG. 3, which is similar to FIG. 2 but with the internal componentsof the plunger section removed for clarity. As shown in FIG. 3, theplunger bore 28 and the access bore 34 comprise respective centerlinesC_(P) and C_(A) which are coaxial along an axis X, and the suction bore36 and the discharge bore 38 comprise respective centerlines C_(S) andC_(D) which are coaxial along an axis Z that is perpendicular to theaxis X. In this embodiment of the fluid end 14, the suction bore 36intersects the plunger bore 28 along a first curve 68, and the dischargebore 38 intersects the plunger bore along a second curve 70. As may beseen in FIG. 3, the curves 68, 70 define relatively sharp edges betweenthe intersecting bores.

During operation of the pump 10, the fluid end 14 is subject to veryhigh frequency and large magnitude pressure pulsations. These pressurepulsations generate large stress concentrations at the boreintersections. In cross-bore geometries in which the bore intersectionsform relatively sharp edges, these stress concentrations may causefatigue cracks to form in the housing proximate the intersections.Traditionally, quasi radii and chamfers have been applied to the boreintersections using hand tools to obtain some semblance of smoothness.With the advent of robotics and multi-axis machines, these features canbe machined programmatically. Although smoothing the bore intersectionsin this manner may reduce the stress concentrations to a certain extent,the cross-bore geometries of extreme service pumping units remainsusceptible to developing excessive stress concentrations due to thelimitations imposed by the current configurations of the boreintersections.

According to the present invention, an improved cross-bore geometry hasbeen developed which greatly reduces the stress concentrations that canlead to fatigue cracks in the fluid end originating at and propagatingfrom the bore intersections. The improved cross-bore geometry isobtained by creating a cross-bore chamber at the intersection of theplunger bore, the access bore, the suction bore and the discharge bore.The characteristics of the cross-bore chamber will be described withreference to the schematic representation shown in FIG. 4. Thecross-bore chamber, generally 72, is configured as a surface ofrevolution which is created by rotating a two-dimensional curve 74around one of the X, Y or Z axes. In this regard, the X, Y and Z axesare defined as the reference axes for the surface of revolution.Although in certain embodiments of the invention the X axis may becoaxial with one or both of the plunger bore centerline C_(P) and theaccess bore centerline C_(A) and the Z axis may be coaxial with one orboth of the suction bore centerline C_(S) and the discharge borecenterline C_(D), these axes do not necessarily have to be aligned withany of the bore centerlines.

The two-dimensional curve 74 can have any practical configuration,provided that it comprises a diameter which is greater than the diameterof the largest of the plunger bore 28, the access bore 34, the suctionbore 36 and the discharge bore 38. In the specific embodiment of theinvention illustrated in FIG. 4, the curve 74 is an ellipse which iscentered at the origin O of the X, Y and Z axes. Thus, the surface ofrevolution defining the cross-bore chamber 72 has the general shape ofan ellipsoid which is centered about the origin O and is created byrotating the ellipse 74 about the X axis. In the context of the presentinvention, however, the ellipsoid may have any configuration which isdefined by the following standard equation:

x ² /a ² +y ² /b ² +z ² /c ²=1,

where a, b and c are the respective lengths of the semi-principal axesof the ellipsoid. For example, the cross-bore chamber 72 may beconfigured as a sphere by making a=b=c.

Referring still to FIG. 4, the intersection of each of the plunger bore28, the access bore 34, the suction bore 36 and the discharge bore 38with the cross-bore chamber 72 defines a respective cross curve 28 a, 34a, 36 a and 38 a. The particular shape of each cross curve will ofcourse depend on the shape of the surface of revolution which definesthe cross-bore chamber 72. As may be seen in FIG. 4, by configuring thecross-bore chamber 72 as a surface of revolution such as an ellipsoid,the cross-bore chamber provides a single, smooth contiguous connectingsurface between each of the cross curves. This single, smooth contiguousconnecting surface is created by virtue of the fact that, rather thanintersecting each other, the plunger bore 28, the access bore 34, thesuction bore 36 and the discharge bore 38 intersect the cross-borechamber 72. Thus, in the present invention the sharp edge formed by theintersection of, e.g., the discharge bore with the plunger bore, iseliminated. Instead, the smooth contiguous connecting surface formed bythe cross-bore chamber 72 extends around and between the cross curves 28a, 34 a, 36 a and 38 a. As a result, the stress concentrations in thecross-bore geometry are significantly reduced, and the fluid end istherefore less susceptible to fatigue crack formation.

Referring to FIGS. 5 and 6, an embodiment of the invention is shown inwhich the cross-bore chamber 72 comprises a spherical configuration. Inthis embodiment, the plunger bore centerline C_(P) and the access borecenterline C_(A) are coaxial with the X axis and the suction borecenterline C_(S) and the discharge bore centerline C_(D) are coaxialwith the Z axis. As may be seen especially in FIG. 5, the sphericalconfiguration of the cross-bore chamber 72 forms a single, smoothcontiguous connecting surface 76 between and around the cross curves 28a, 34 a, 36 a and 38 a. In this embodiment, the bore with the largestdiameter is the suction bore 36, and the sphere defining the cross-borechamber 72 comprises a diameter which is larger than the diameter of thesuction bore. In this as in other embodiments of the invention, theshape and size of the surface of revolution which is used to form thecross-bore chamber 72 may be determined empirically for a particularcross-bore geometry in order to provide desired stress and flowcharacteristics for the fluid end.

Further illustrative and non-limiting embodiments of the cross boregeometry of the present invention are shown in FIGS. 7-9. The cross boregeometry shown in FIG. 7 is similar to that shown in FIG. 6. In theembodiment shown in FIG. 7, however, the X axis is offset from theplunger bore centerline C_(P) and the access bore centerline C_(A),which in this case are coaxial. In this example, where the cross-borechamber 72 is defined by a sphere having a diameter of 8.50″, the X axisis offset in the Z direction 0.50″ from the plunger bore centerlineC_(P) toward the suction bore 36.

In the embodiment of the cross-bore geometry shown in FIG. 8, the X axisis coaxial with the plunger bore centerline C_(P) and the access borecenterline C_(A), but the Z axis is offset from the suction borecenterline. C_(S) and the discharge bore centerline C_(D), which in thisinstance are coaxial. In this example, where the cross-bore chamber 72is defined by a sphere having a diameter of 8.50″, the Z axis is offsetin the X direction 0.20″ from the discharge bore centerline C_(D) towardthe access bore 34.

In the embodiment of the cross-bore geometry shown in FIG. 9, the X axisis offset from the plunger bore centerline C_(P) and the access borecenterline C_(A), which in this instance are coaxial, and the Z axis isoffset from the suction bore centerline C_(S) and the discharge borecenterline C_(D), which in this case are also coaxial. In this example,where the cross-bore chamber 72 is defined by a sphere having a diameterof 8.50″, the X axis is offset in the Z direction 0.50″ from the plungerbore centerline C_(P) toward the suction bore 36, and the Z axis isoffset in the X direction 0.20″ from the discharge bore centerline C_(D)toward the access bore 34.

Another example of a fluid end in which the cross-bore geometry of thepresent invention may be incorporated is shown in FIG. 10. The fluid endof this embodiment, generally 14′, is described more fully in U.S. Pat.No. 8,147,227, which is hereby incorporated herein by reference. Asshown in FIG. 10, the fluid end 14′ comprises a Y-shaped cross borearrangement in which the access bore is omitted and the plunger bore 26,the suction bore 36 and the discharge bore 38 are oriented approximately120° from each other.

In accordance with the present invention, a cross-bore chamber (notshown) may be machined into the fluid end to provide the advantagesdescribed above. As in the previous embodiments, the cross-bore chambermay comprise a surface of revolution, such as an ellipsoid, which iscentered at the origin O of the X, Y and Z reference axes. In addition,the X axis may be either aligned with or offset from the plunger borecenterline C_(P), and the origin O of the reference axes may be locatedat or offset from the intersection of the plunger bore centerline C_(P),the suction bore centerline C_(S) and the discharge bore centerlineC_(D).

It should be recognized that, while the present invention has beendescribed in relation to the preferred embodiments thereof, thoseskilled in the art may develop a wide variation of structural andoperational details without departing from the principles of theinvention. Therefore, the appended claims are to be construed to coverall equivalents falling within the true scope and spirit of theinvention.

We claim:
 1. In a reciprocating pump comprising a fluid end housinghaving a number of plunger sections, each plunger section including aplunger bore within which a plunger is slidably received, a suction borewithin which a suction valve is positioned and a discharge bore withinwhich a discharge valve is positioned, the improvement comprising across bore chamber which is located between said bores and is configuredas a surface of revolution, wherein each of said bores intersects thecross-bore chamber to thereby define a respective cross curve which isspatially separated from each adjacent cross curve, whereby thecross-bore chamber defines a single, contiguous surface which extendsaround and between all of said cross curves.
 2. The pump of claim 1,wherein the cross-bore chamber is configured as an ellipsoid.
 3. Thepump of claim 2, wherein the ellipsoid comprises a first axis which iscoaxial with a centerline of the plunger bore and a second axis which iscoaxial with at least one of a centerline of the suction bore and acenterline of the discharge bore.
 4. The pump of claim 2, wherein theellipsoid comprises a first axis which is coaxial with a centerline ofthe plunger bore and a second axis which is parallel to but offset fromat least one of a centerline of the suction bore and a centerline of thedischarge bore.
 5. The pump of claim 2, wherein the ellipsoid comprisesa first axis which is parallel to but offset from a centerline of theplunger bore and a second axis which is coaxial with at least one of acenterline of the suction bore and a centerline of the discharge bore.6. The pump of claim 2, wherein the ellipsoid comprises a first axiswhich is parallel to but offset from a centerline of the plunger boreand a second axis which is parallel to but offset from at least one of acenterline of the suction bore and a centerline of the discharge bore.7. The pump of claim 1, wherein each plunger section further comprisesan access bore which intersects the cross-bore chamber to thereby definea corresponding cross curve that is spatially separated from eachadjacent cross curve, whereby the cross-bore chamber defines a single,contiguous surface which extends around and between all of said crosscurves.
 8. The pump of claim 7, wherein the cross-bore chamber isconfigured as an ellipsoid.
 9. The pump of claim 8, wherein the accessbore is generally aligned with the plunger bore and the suction bore isgenerally aligned with the discharge bore, and wherein the access andplunger bores are oriented at an angle of generally ninety degreesrelative to the suction and discharge bores.
 10. The pump of claim 9,wherein the ellipsoid comprises a first axis which is coaxial with acenterline of the plunger bore and a second axis which is coaxial withat least one of a centerline of the suction bore and a centerline of thedischarge bore.
 11. The pump of claim 9, wherein the ellipsoid comprisesa first axis which is coaxial with a centerline of the plunger bore anda second axis which is parallel to but offset from at least one of acenterline of the suction bore and a centerline of the discharge bore.12. The pump of claim 9, wherein the ellipsoid comprises a first axiswhich is parallel to but offset from a centerline of the plunger boreand a second axis which is coaxial with at least one of a centerline ofthe suction bore and a centerline of the discharge bore.
 13. The pump ofclaim 9, wherein the ellipsoid comprises a first axis which is parallelto but offset from a centerline of the plunger bore and a second axiswhich is parallel to but offset from at least one of a centerline of thesuction bore and a centerline of the discharge bore.
 14. The pump ofclaim 2, wherein each of said bores is oriented at an angle ofapproximately 120 degrees relative to each other bore.
 15. The pump ofclaim 14, wherein the ellipsoid comprises a first axis which is coaxialwith a centerline of the plunger bore and a center point which islocated at an intersection of the plunger bore, the suction bore and thedischarge bore.
 16. The pump of claim 14, wherein the ellipsoidcomprises a first axis which is coaxial with a centerline of the plungerbore and a center point which is offset from an intersection of theplunger bore, the suction bore and the discharge bore.
 17. The pump ofclaim 14, wherein the ellipsoid comprises a first axis which is parallelto but offset from a centerline of the plunger bore and a center whichis located at an intersection of the plunger bore, the suction bore andthe discharge bore.
 18. The pump of claim 14, wherein the ellipsoidcomprises a first axis which is parallel to but offset from a centerlineof the plunger bore and a center which is offset from an intersection ofthe plunger bore, the suction bore and the discharge bore.
 19. A methodof reducing stress concentrations in a fluid end housing of areciprocating pump, the fluid end housing having a number of plungersections, each plunger section including a plunger bore within which aplunger is slidably received, a suction bore within which a suctionvalve is positioned and a discharge bore within which a discharge valveis positioned, the method comprising: forming a cross-bore chamberbetween said bores, said cross-bore chamber being configured as asurface of revolution; wherein each of said bores intersects thecross-bore chamber to thereby define a respective cross curve which isspatially separated from each adjacent cross curve; whereby thecross-bore chamber defines a single, contiguous surface which extendsaround and between all of said cross curves.
 20. The method of claim 19,wherein said cross-bore chamber is configured as a spheroid.